1. Field of the Invention
The present invention relates to an image pickup apparatus provided with an image sensing means by which pixel data of a half of all the pixels can be read out in one read-out operation, and more particularly, it relates to an image pickup apparatus suitable for a video camera provided with a function of recording still pictures on a memory card.
2. Description of the Related Art
FIG. 1 shows a system block diagram of a conventional video camera.
In FIG. 1, a light from a subject etc. passes through a lens system 99 provided with a focusing mechanism (not shown) and then a complementing filter in which Cy (cyan), G (green), Ye (yellow), and Mg (magenta) color filters are arranged corresponding to their respective pixels and then is made incident on a CCD (Charge Coupled Device) 101.
The CCD 101 is of an inter-line type, i.e. it is driven for field read-out by a drive signal from a timing generator (TG) 104. That is, from the CCD 101 driven by the timing generator 104 are read out picked-up image signals of vertically adjacent pixels as mixed on this CCD.
More specifically, as shown in FIG. 2, in the first field for example, the picked-up image signals of pixels respectively corresponding to vertically adjacent color filters of Cy+G, Ye+Mg, Cy+G, Ye+Mg, . . . in an A1 line are mixed on this CCD and read out, after which the picked-up image signals of pixels respectively corresponding to vertically adjacent color filters of Cy+Mg, Ye+G, Cy+Mg, Ye+G, . . . in the next A2 line are mixed on this CCD and read out. Subsequently, also for each of an A3 line, an A4 line, (not shown), the picked-up image signals of the vertically adjacent pixels are mixed and read out in the same manner. Furthermore, in the second field, the picked-up image signals respectively corresponding to the vertically adjacent color filters of G+Cy, Mg+Ye, G+Cy, Mg+Ye, . . . in a B1 line are mixed on the CCD and read out, and then, the picked-up image signals of the vertically adjacent pixels for each of a B2 line, a B3 line, . . . lines are also mixed and read out in the same manner. The picked-up image signals output from this CCD 101 are sent to a CDS/AGC (Correlation Double Sampling/Automatic Gain Control) circuit 102.
The CDS/AGC circuit 102 utilizes correlation double sampling (CDS) processing, to remove noise from the picked-up image signal, and it also utilizes automatic gain control (AGC) processing, to control the gain of the picked-up image signal at a desired value. The picked-up image signal output from the CDS/AGC circuit 102 is sent to an ADC (A/D converter) circuit 103.
The ADC circuit 103 converts an analog picked-up image signal output from the CDS/AGC circuit 102 into digital picked-up image data (A/D conversion). The picked-up image data output from the ADC is sent to a DSP (Digital Signal Processor) 116 enclosed by a dotted line in FIG. 1.
The DSP 116 performs the following various signal processes in response to an instruction sent from a camera microcomputer 105.
The picked-up image data input into the DSP 116 is first sent to a Y/C separating unit 106. The Y/C separating unit 106 separate thus supplied picked-up image data into brightness data and color data. The output data from the Y/C separating unit 106 is sent to an IWD (Horizontal Pixel Extraction) unit 107.
The IWD unit 107 extracts only the data corresponding to each pixel which provides a horizontal effective pixel on the CCD 101, based on camera shake information including a quantity of camera shake and a velocity of camera shake. That is, the IWD unit 107 extracts only such data of those data pieces corresponding to each pixel on the CCD 101 that lies in a direction in which the camera shake can be corrected.
The data output from the IWD unit 107 is sent from a signal switching unit 108.
The signal switching unit 108, in response to, for example, an instruction from the camera microcomputer 105, makes switching between data output from the IWD unit 107 and reproduction data sent from a later-mentioned recording/play-back device 114 and then sends thus selected data to an FMC (Video Memory Controller) unit 109. That is, for example, when data of pictures which are being imaged by this video camera is recorded by the recording/play-back device 114 or when this data is output as it is to the outside as a video signal, the signal switching unit 108 is set to send the output data of the IWD unit 107 to the FMC unit 109; on the other hand, when the reproduction data is output from the recording/play-back device 114 to outside as a video signal, the signal switching unit 108 is set to send the reproduction data of the recording/play-back device 114 to the FMC unit 109.
The FMC unit 109 controls read/write operations of data to a VRAM 113 serving as a video memory. In this case, the read/write operations of data to the VRAM 113, am controlled by the FMC unit 109 for the purpose of, for example, fine adjustment in correction for camera shake, and the realization of-various production effects on the picture.
The fine adjustment in correction for camera shake here means to perform camera shake correction processing based on camera shake information with a precision of less than two horizontal pixels in one line. Accordingly, the FMC unit 109 controls data read/write operations to the VRAM 113 to perform the fine adjustment in correction for camera shake with a precision of less than two horizontal pixels in one line. Furthermore, as the production effects on the pictures, specifically, the generation of, for example, still pictures such as souvenir photographs, multi-pictures in which a plurality of pictures are arranged on one screen, sepia-tone pictures, and black-and-white pictures, and the image processing such as fading and wiping may be employed. Therefore, the EMC unit 109 reads out data from the VRAM 113 which is necessary for realization of these production effects. The data thus read out by the FMC unit 109 from the VRAM 113 is sent to a YNR (Brightness Signal Noise Reducer) unit 110.
The YNR unit 110 suppresses the noise of brightness data. The data output from this YNR unit 110 is sent to the recording/play-back device 114 as demanded by a user of this video camera, to be recorded, for example, on such a recording medium as a magnetic tape, a magnetic disk, or an optical disk or it is sent to an ENC (Color Encoder) unit 111 to be output to outside as a video signal.
The ENC unit 111 converts thus supplied data into a signal conforming to such TV broadcasting scheme as, for example, NTSC (National Television System Committee), PAL (Phase Alternation by Line), SECAM (Sequential Couleur a Memoirs), etc. The signal from this ENC unit 111 is sent to a DAC (D/A converter) unit 112.
The DAC unit 112 converts the data from the ENC unit 25 111 into an analog video signal. The video signal from the DAC unit 112 of the DSP 116 is output to outside from an output terminal 115.
The recording/play-back device 114, on the other hand, responds to a demand from the user of this camera, to reproduce the data previously recorded on the recording medium, thereby sending the reproduction data to the signal switching unit 108. The reproduction data supplied to the signal switching unit 108 passes through the EMC unit 109, the YNR unit 110, the ENC unit 111, and the DAC unit 112 and then is output to outside as a video signal from the output terminal 115.
Next, FIG. 3 shows a system block diagram of a conventional digital camera (digital still camera).
In FIG. 3, a light from a subject passes through a lens mechanism 117 driven by a focusing mechanism 118 capable of auto-focusing, an irising mechanism 119 capable of auto-irising, and a complementing filter 120 in which Cy (cyan), G (green), Ye (yellow), and Mg (magenta) color filters are arranged and then is made incident on a CCD 121.
The CCD 121, which is of a progressive scanning type, is driven for frame read-out by a drive signal from the timing generator (TG) 124. That is, in contrast to the above-mentioned example of FIG. 1, from the CCD 121 driven by this timing generator 123 are read out the picked-up image signals of the respective CCD pixels without being mixed.
More specifically, as shown in FIG. 4, the picked-up image signals of all the pixels are read out from the CCD in such an order as those for the pixels corresponding to the CY, Ye, Cy, . . . color filters in a line a1, the pixels corresponding to the Cy, Ye, Cy, Ye, . . . color filters in a line a2, and the pixels corresponding to the G, Mg, G, Mg, . . . color filters. The picked-up image signals thus output from the CCD 121 are sent to a CDS/AGC circuit 122.
The CDS/AGC circuit 122, as in the configuration of FIG. 4, utilizes correlation double sampling processing to removes noise and also automatic gain control processing to control the gain of the picked-up image signal at a desired value. The picked-up image signal output from this CDS/AGC circuit 102 is converted at the ADC circuit 103 into digital picked-up image data and then sent to a DSP 139 enclosed by a dotted line in FIG. 3.
The DSP 139 performs the following various signal processes.
The picked-up image data input to the DSP 139 is first sent to a DMACTL (DMA controller) unit 127. The DMACTL unit 127 transfers the picked-up image data of one screen in a DMA (Direct Memory Access) manner to a memory in a microcomputer 125.
The microcomputer 125 utilizes software processing to separate the picked-up image data thus supplied from the DMACTL unit 127 into brightness data and color data, to generate still-picture data. The still-picture data thus generated by the microcomputer 125 again passes through the DMACTL unit 127 in DMA transfer up to a DRAMCTL (External Memory Controller) unit 128.
The DRAMCTL unit 128 controls the read/write operations of data to a DRAM 133 serving as the external memory. At this point in time, the DRAMCTL unit 128 writes to the DRAM 133 the still-picture data supplied via the DMACTL unit 127 from the microcomputer 125. Furthermore, the DRAMCTL unit 128 always reads out the still-picture data, from the DRAM 133 even when the microcomputer 125 is executing other processing, thus sending that still-picture data to an FCNV (Clock Converter) unit 129.
The FCNV unit 129 converts the clock signal for still-picture data from the clock signal used in the microcomputer 125 into a clock signal used at the following-stage ENC unit 131; Output data from the FCNV unit 129 is sent to a YNR (Brightness Signal Noise Reducer) unit 130.
The YNR unit 130 suppresses the noise of the brightness 25 data.
Data output from the YNR unit 130 is sent to the ENC unit 131.
The ENC unit 131 converts thus supplied data into a signal conforming to such a TV broadcasting scheme as NTSC, PAL, or SECAM. The signal from the ENC unit 131 is sent to a DAC unit 132.
The DAC unit 132 converts the data from the ENC unit 121 into an analog video signal. The video signal output from the DAC unit 132 of the DSP 139 is output to outside from an output terminal 138. Furthermore, the still-picture data generated by the microcomputer 125 undergoes picture compression processing by use of software processing in response to a demand from the user of this digital camera and then is recorded on a detachable memory card 126 provided with a semiconductor memory. The compressed data recorded on the memory card 126 is read out from the memory card 126 in response to a demand from this digital camera user and then taken into the microcomputer.
The microcomputer 125, after thus taking in the compressed data from the memory card 126, decompresses that data using software processing, to restore still-picture data. The still-picture data thus restored by the microcomputer 125 passes through the DMACTL unit 127 in DMA transfer and is sent to the DRAMCTL unit 128. The still-picture data thus sent to the DRAMCTL unit 128 passes through, in almost the same manner as mentioned above, the FCNV unit 129, the YNR unit 130, the ENC unit 131, and the DAC unit 132 and then is output from the output terminal 138 as a video signal.
Furthermore, at the digital camera shown in FIG. 3, the still-picture data restored by the microcomputer 125 can be transferred, for example, to a personal computer by, for example, infrared communications by an IrDA (Infrared Communication) unit 134, asynchronous serial communications by a USART (Asynchronous Serial Communication) unit 135, or serial communications by a PORT unit 137. A TIMER (Timer) unit 136 is provided for generating date-and-time information, which is added to each still picture as a photography date and time.
At the digital camera shown In FIG. 3. still-picture data transferred, for example, from a personal computer in infrared communications can be received at the IrDA unit 134, still-picture data transferred, for example, from a personal computer in asynchronous serial communications can be received at the UART unit 135, and also still-picture data transferred, for example, from a personal computer in serial communications can be received by the PORT unit 137.
The above-mentioned conventional video camera shown in FIG. 1 uses a field-read-out type CCD, thus suffering from a disadvantage of a rather low vertical resolution of about 240 pixels of a field still picture. Moreover, the video camera of FIG. 1 configures a frame picture of two field pictures, so that such a frame still picture thus made of two field pictures has a problem of, for example, doubling of a moving subject because of a difference in time between these two field pictures. That is, according to the NTSC scheme, for example, two field pictures have a mutual time difference of 1/60 second, so that one still picture generated of these two field pictures would have the image shift of 1/60 second.
The conventional digital camera shown in FIG. 3, on the other hand, uses a frame-read-out type CCD, so that it, can enjoy a high vertical resolution and also obtain a still picture without doubling of a moving subject. The frameread-out type CCD, however, is generally more expensive than the field-read-out type CCD and cannot easily by lowered in costs.
Furthermore, the above-mentioned conventional digital camera shown in FIG. 3 requires rather long time in processing because it always uses software programs to execute processes of the separation of picked-up image data into brightness data and color data as well as also various automatic control processes of, for example, the auto-focus control by the focusing mechanism 118, the auto-iris control by the irising mechanism 119, and the auto-white balancing.